The paper discusses the impact of the Pinatubo simulation on tropospheric chemistry. To validate the evolution of stratospheric aerosols, panal a) show simulated and panel b) lidar observed stratospheric aerosol backscatter profile at 694.3 nm at Mauna Loa station [Barnes and Hofmann, 1997]. Results are shown for the first two years after the eruption, and show the global spread of aerosols.